1. Field of the Invention
The present invention relates to sieving coarse particles from powder using a filter.
2. Description of the Related Art
Conventionally, a method for visualizing image information using a toner has been utilized in various fields. For example, in an image forming apparatus employing electrophotography, image information is visualized as follows. Specifically, a latent electrostatic image is formed on a photoconductor based on image information and developed with a developer containing a toner to form a toner image, which is then transferred and fixed on a paper sheet.
In recent years, small-particle-diameter toners have been used as the toner used in an image forming apparatus, in order to obtain high-quality images. Such toners may contain coarse particles in the production process. Alternatively, they may contain coarse particles which formed through loose aggregation caused during storage under high-temperature, high-humidity conditions. The toner containing such coarse particles cannot accurately develop a toner image based on image data.
In view of this, a sieving device has been used for sieving coarse particles contained in toner. One known sieving device which sieves coarse particles from toner is an ultrasonic sieve (see Japanese Patent Application Laid-Open (JP-A) No. 2006-23782). The ultrasonic sieve is configured to vibrate a filter with ultrasonic waves to thereby sieve coarse particles contained in toner. However, sieving by the ultrasonic sieve causes the following problems: filter clogging caused by softening of the toner due to frictional heat generated by vibrating the filter; and expansion of the openings of the filter due to stress applied by the vibration.
In view of this, there has been proposed a sieving device for sieving coarse particles from powder without vibrating a filter (see JP-A No. 2009-90167). This sieving device contains: a rotary shaft disposed in a predetermined direction; a cylindrical sieve disposed axially to the rotary shaft; and a rotary blade attached to the rotary shaft. This can sieve powder without vibrating the sieve according to the following mechanism: the rotary blade is rotated to feed powder, which has been supplied from upstream, from the inner region to the outer region of the cylindrical sieve.
However, the sieving device containing the cylindrical sieve requires a large space for collecting the powder having passed through the sieve, since it has the above-described mechanism of feeding the powder from the inner region to the outer region of the cylindrical sieve. That is, use of the cylindrical sieve problematically enlarges the sieving device.
Also, when the sieving device containing the cylindrical sieve is mounted in an image forming apparatus for sieving coarse particles from toner supplied from a developing device of the image forming apparatus, the image forming apparatus is problematically enlarged.
Furthermore, when the sieving device containing the cylindrical sieve is mounted in a powder-charging device for charging powder into a predetermined container, the powder-charging device is problematically enlarged.